Concentric cable with mineral insulation



March 23, 1937. M J coup 2,074,777

CONCENTRIC CABLE WITH MINERAL INSULATION Filed March 14, 1935 5 Zea/var? Patented M". 23, 1937 UNITED STATES conoan'rmc CABLE wrrn mm.

msum'non Marcel Marie Joseph Eugene Coupler, Paris, France Application March 14, 1935, Serial No. 11,156 In France March 14, 1934 2 Claims.

It is well known that electric conductors may consist of a central conductor embedded in a mineral insulating material the whole being surrounded by a metallic covering disposed around 5 said insulating material; this latter may be for instance magnesia obtained by submitting magnesium to a suitable treatment in situ"; the whole is further mechanically treated by rolling, drawing or the like, in order to give it finally the 1 length and diameter desired.

This procedure makes it possible to obtain good results for single wire cable under a metallic, e. g. lead, covering, but it cannot be easily applied to multiple conductor cables. This is due to the 15 fact that during the lengthening by rolling, drawing or the like, the radial strains would not be applied to a medium which is radially uniform since certain radii meet the conductors and others only the insulating material; said strain would 20 consequently produce different 'efiects and at the ,end ofthe operation it might occur that the initial arrangement of the different conductors is altered. On the other hand if the cable were bent the conductors and insulating material 25 would'behave in diilerent ways according to the direction of the plan of the curve with reference to the conductors.

My present invention has for its object a concentric cable with mineral insulation character- 30 ized by the fact that it contains a solid central conductor surrounded by one or more coaxial tubular conductors, the ring shaped spaces between the different conductors, as well as the space between the last conductor and the cover- 35 ing, being ultimately filled with a mineral powder,

e. g. magnesia.

In such a cable on one hand the radial strains exerted during the lengthening by rolling, drawing or the like are applied to an absolutely uni- 40 form medium, and on the other hand when the cable is bent the position of the plan of the curve is of no consequence.

By way of example, in the appended drawing I have represented the cross-section of a two con- 45 ductor cable according to my invention, constituted by a central cylindrical conductor i and a tubular conductor 2 separated from each other by a layer 3 of powdered insulating material; the whole being protected by an outer metallic cov- 50 ering 4, separated from tubular conductor 2 by another layer 5 of mineral powder.

By way of example the cable represented in the figure may be manufactured by covering the central conductor with one or more helical windings 55 of magnesium wires or tubes; by disposing the resultant whole inside the tubular conductor 2, covering this latter with magnesium wires or tapes as explained above; this whole is then introduced into the covering and steam is caused to flow through the ring shaped spaces 3 and 5 5 whereupon the magnesium is transformed into hydroxide, and further, by heating, into magnesia which expands and fills said spaces almost entirely; the resultant whole is then submitted to rolling, drawing or the like in order to give there to the desired length and diameter.

It is also possible to proceed in a slightly different way. The central conductor around which are wound the magnesium wire or wires, is disposed inside the tubular conductor 2 and the magnesium transformed into magnesia by the action of steam and heat. The resultant whole is then rolled or drawn so that it receives a length intermediate its original length and the desired final length. Thereupon, magnesium wires are wound on conductor 2 and the whole is disposed inside the covering. The magnesium is treated by steam, which, this time, does not fiow through space 3 already filled with magnesia; the whole is finally rolled or drawn in order to give thereto its definitive dimensions.

It is obviously possible to prepare cables with more than two conductors in this manner; e. g. threephase cables provided with a central conductor the section of which should be smaller than that of the other and which may be used as neutral wire.

What I claim is:

1. A multi-stage method for the manufacture of a magnesia-insulated multiple conductor cable comprising a first stage consisting in substantially encasing a wire which constitutes a first conductor in magnesium windings, then enclosing the said wire and windings in a tubular metallic member of larger diameter which constitutes a second conductor, then passing a fiow of steam between the said two conductors whereby the magnesium is converted into hydroxide form, then heating the whole to convert the hydroxide into magnesia, and finally subjecting the whole to a mechanical lengthening treatment, said treatment being terminated before a length corresponding to the ultimate length of the cable is attained, and a subsequent stage consisting in substantially encasing the product of the preceding stage in magnesium windings, then enclosing the windings in a tubular metallic member of larger diameter, then passing a flow of steam through the magnesium to convert it into hydroxide form, then heating the whole to convert the hydroxide into magnesia and finally subjecting the whole to a mechanical lengthening treatment-so as to give it the final length desired for the. cable.

2. A multi-stage method for the manufacture of a magnesia-insulated multiple conductor cable comprising a first stage. consisting in substantially encasing a wire which constitutes a first conductor in magnesium windings, then enclosing the said wire and windings in a tubular metallic member of larger diameter which constitutes a second conductor, then passing a flow of steam between the said two conductors whereby the magnesium is converted into hydroxide form, then heating the whole to convert the hydroxide into magnesia, and finally subjecting the whole to a mechanical lengthening treatment, said treatment being terminated before a length corresponding to the ultimate length of the cable is attained; and subsequent stages, each or which consists in substantially encasing the product of the preceding stage in magnesium windings, then enclosing the windings in a tubular metallic member of larger diameter, then passing a fiow of steam through the magnesium to convert it into hydroxide form, then heating the whole to convert the hydroxide into magnesia and finally subjecting the whole to a mechanical lengthening treatment, the tubular metallic'members used in the said subsequent stages constituting conductors except the last tubular member which constitutes the covering oi the cable, the mechanical lengthening treatments of the said subsequent stages except the last one being such as to impart to the product submitted thereto a length less than the final length desired for the cable, said final length being reached by the mechanical lengthening treatment of the. last stage. 

